This invention relates to the field of liquid detergent compositions suitable for use in automatic dishwashers.
Compositions for use in automatic dishwashers are formulated with different objectives than other types of detergents. The chief objectives are the removal of food soils, the removal of stains, and the destruction of bacteria.
The removal of food soils is both mechanical and physico-chemical in nature and is influenced by a number of factors among which are wetting, emulsification, adhesion of soil to substrate, soil suspension, alkalinity, anti-flocculation and foam control. Wetting and emulsification can be achieved with many common surfactants, but other considerations must be taken into account. The removal of soils is best effectuated with large amounts of builder and high pH. In order to increase the pH, large amounts of highly alkaline inorganic salts such as hydroxides, carbonates and metasilicates are present, which cause the saponification of fatty soils. This high pH-surfactant system is assisted by vigorous mechanical action. Protein soils have a tendency to foam under this heavy mechanical action and this foam impedes the mechanical cleaning action of the dishwasher and may cause the machine to overflow. In order to minimize foaming, certain low foaming surfactants are chosen to formulate dishwasher compositions and foam suppressants may be added.
Dishwasher detergents generally take the form of free flowing powder granules which are dispensed from cups which are built into most machines. Due to the high pH and frangibility of these powders, dusty fines are often produced which can cause sneezing, eye irritation and dermatitis. These powders tend to cake when exposed to air for long periods of time and become less soluble after aging; due to absorption of carbon dioxide from the air, the pH drops converting some of the silicate to insoluble silica. This reduced solubility often results in grittiness and spotting of washed articles.
Liquid dishwasher detergents have not thus far been commercialized for home use. The ideal liquid dishwasher detergent must be dispensible from the means currently installed in dishwashers for dispensing powders. This requires that such a liquid have a fairly high viscosity so that it will not run out of a loosely sealed dispensing cup meant for powders, when the dishwasher door is closed. Ordinary hand dishwashing liquids have low viscosity and high foam and are thus unsuitable. The ideal product, despite its high viscosity, must flow easily so that it may be dispensed from a tube or plastic squeeze bottle. The product must also completely dissolve in water very quickly and must not separate upon standing.
In order to achieve viscosities as high as are desired in a system such as this, it is useful to use thickening agents. However, the other system parameters, the high pH and high electrolyte content make the use of a thickening agent difficult, since thickening agents generally do not remain stable under these conditions. In addition, in gum thickened systems of very high viscosities, it is difficult to attain satisfactory flow properties, the result often being a stringy or gummy mass.